.TP
.B 1.1
Enforce HTTP 1.1 requests.
+.TP
+.B 2.0
+Enforce HTTP version 2 requests.
+.TP
+.B 2TLS
+Enforce version 2 requests for HTTPS, version 1.1 for HTTP.
+.TP
+.B 2_PRIOR_KNOWLEDGE
+Enforce HTTP 2 requests without performing HTTP/1.1 Upgrade first.
.RE
.TP